Rotating blades in a blade assembly may experience bending, twisting, and aerodynamic forces that can lead to a blade moving out-of-plane with respect to the other blades, or experience a lead/lag effect where uniform phase between the respective blades is not maintained. In the case of turbine blades installed on a disk, that blade lead or lag can lead to the blade assembly misbalance and damage. In the case of helicopter main rotor blades, excessive out of track or lead/lag can indicate or facilitate premature wear of the blade retention assemblies & components. Ideally, a blade's track and/or lead/lag needs to be detected with accuracy of 1-2 mm in the case of rotating helicopter blades.